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Charge Order and Negative Thermal Expansion in V2OPO4
Elise Pachoud1, James Cumby1, Calum T Lithgow1
1Centre for Science at Extreme Conditions and School of Chemistry, University of Edinburgh , Edinburgh EH9 3FD, United Kingdom.
Journal of the American Chemical Society
|December 21, 2017
Summary
Semivalent oxyphosphate V2OPO4 exhibits charge ordering up to 605 K, showing a structural transition and a switch in thermal expansion. V-V bonding loss drives this novel behavior, alongside ferrimagnetic ordering below 164 K.
Area of Science:
- Solid State Chemistry
- Materials Science
- Magnetism
Background:
- Understanding charge ordering and its impact on material properties is crucial.
- Investigating novel materials with switchable thermal expansion is of significant interest.
Purpose of the Study:
- To investigate the charge ordering and thermal expansion properties of semivalent oxyphosphate V2OPO4.
- To elucidate the relationship between V-V bonding, structural transitions, and thermal expansion behavior.
- To explore the magnetic ordering in V2OPO4.
Main Methods:
- X-ray diffraction for structural analysis.
- Dilatometry for thermal expansion measurements.
- Magnetic susceptibility measurements for magnetic ordering studies.
Main Results:
- Long-range V2+/V3+ charge ordering observed up to 605 K.
- Monoclinic to tetragonal structural transition at 605 K.
- Switch from positive to negative thermal expansion observed.
- Ferrimagnetic order below a magnetic ordering transition at 164 K.
- Evidence of local spin pairing correlations at higher temperatures.
Conclusions:
- V-V bonding within orbital polymer chains is key to the switchable thermal expansion.
- Loss of V-V bonding allows transverse oxygen motions to dominate thermal expansion at high temperatures.
- V2OPO4 exhibits complex interplay between charge ordering, structure, and magnetism.
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